Asthma is a condition that affects the airways – the small tubes that carry air in and out of the lungs - and the symptoms are generally coughing, wheezing, shortness of breath and chest tightness. The symptoms can be occasional or persistent. When a person with asthma breathes in an asthma trigger (something that irritates their airways), the muscles around the walls of the airways tighten so that the airways become narrower and the lining of the airways becomes inflamed and starts to swell. For many people with asthma, cold and flu viruses trigger their symptoms. Therefore, getting a flu virus makes their asthma worse and having a flu jab (influenza vaccine) may protect people against some of the flu viruses that they will come into contact with in a given winter. However, the effects of a flu jab (vaccination) are not straightforward as there is also the possibility that the flu jab itself could cause a worsening of asthma. Current guidelines in the UK recommend that high-risk groups such as people with severe asthma should have a flu jab each winter (NHS Choices); however, there is limited evidence for this approach.
In this review, we evaluated evidence from randomised trials (RCTs) in relation to potential benefits and harms of all types of influenza vaccination in adults and children (over the age of two years) with asthma.
One trial in 696 children assessed the benefits of injecting inactivated influenza vaccine (inactivated virus vaccines are the type currently used in the US and UK and cannot cause flu). There were no significant differences in the number of people experiencing an asthma attack (worsening of symptoms); however, there were better symptom scores (people reporting fewer asthma symptoms) in weeks in which children had a positive test for influenza, in those who had received the jab compared to those who did not.
Two trials involved 1526 adults and 712 children who were given inactivated influenza vaccination, examined the harmful effects caused immediately after injection. These studies ruled out the likelihood of any more than four out of 100 people having a resultant asthma attack in the first two weeks after getting their flu jab. There was not enough information to compare different vaccination types.